#include<stdio.h>
int main()
{
	int i;
	int count;
	scanf("%d",&i);
	while(i)
	{
		for(;i>0;i--)
		{
			i-1;
			count++;
			if(count%2==0)
			{
				i++;
			}
		} 
	}
	printf("%d",count);
	
	return 0;
 } 
